//1.输出结果
let a = 0;
const obj = {
    A: 1,
    B: function() {
        console.log(this.a);
    }
}
const obj1 = {
    C: 2
}

const fun = obj.B;

fun();

fun.apply(obj);

fun.bind(obj1).apply(obj);

const fun1 = fun.bind(obj1);
new fun()